Such a ventilation ceiling can be found in, for example, the kitchen of a hospital or retirement home. The ceiling contains air supply and air discharge elements, and possibly also light fittings. The air discharge elements increasingly serve the purpose of removing grease etc. from the extracted air, so that they act as air filter elements. For example, to that end the air discharge elements are designed as double-walled coffers which have supply and discharge openings in the walls and grease extractors disposed in said coffers.
Making those air filter elements curved ensures that the constituents filtered out of the air will flow to the side edges of the filter element, where the constituents can be collected, for example, in a collecting element.
DE-A-2949235 discloses, for example, double-curved coffers which are square in top view. Channel parts are detachably disposed below the edges thereof. The idea is to remove those channel parts regularly, in order to clean them. The coffers themselves can be cleaned by removing them from the ceiling and placing them in a dishwasher. Removing the channel parts regularly is troublesome, and is therefore often left undone. In practice, the channel parts are cleaned only when they are full to the brim, and grease and the like is dripping out of them.
In order to make extracting the grease and the like more reliable, an attempt was made to connect the channel parts to a grease-collecting vessel, such as a tank placed on the ground, or the sewerage system. The idea was that the grease end other constituents filtered out of the channel parts would flow out of the channel parts by themselves into the grease-collecting vessel. However, it was found that this did not work in practice: the grease hardly flows any further along in the channel parts. Consequently, there is hardly any grease discharge to the grease-collecting vessel, and the channel parts have become clogged after some time, which leads to leaking again from the channel parts.
The desire to simplify the cleaning of a ventilation ceiling with integral air filter elements and to make such cleaning more reliable has therefore been felt for a long time.
In order to clean the channel parts, a system was proposed in which it is not necessary to remove the channel parts. This system comprises a mobile stock tank with aqueous cleaning agent, a pump and a flexible hose. The idea is to place the outlet of the hose in a channel part by hand, following which aqueous cleaning agent is pumped into the channel part through the hose. It is expected that the cleaning agent will loosen and dissolve the grease and the other constituents in the channel and will take them to the grease-collecting vessel.
Personnel frequently forget to use this known system, with the result that the channel parts become clogged, and can then be cleaned only by mechanical means, so that they still have to be removed. Moreover, only one channel part can be treated at a time. It is necessary to check in each case whether all channel parts have been treated with the system, and the operative himself has to keep an eye on the duration of the flushing. The quality of the flushing is consequently not consistent. In addition, flushing for too long (for example, by forgetting that flushing is going on) is wasteful. Connecting up the system in each case is labour-intensive. Moreover, standing on the ground and inserting the nozzle by hand into the channel parts several meters higher up is difficult and can lead to errors. There is consequently a great risk of the channel parts overflowing. Besides, the system is expensive, since it must have its own pump; and the channel parts and the discharge channel disposed downstream thereof and leading to the grease-collecting vessel are often not designed for flushing with the cleaning agent, so that there is a risk of leakage.